1. Field of the Invention
The present invention relates to an improvement on a crystal holding apparatus for holding a corrugated portion of a crystal in a pulling apparatus which pulls the crystal according to the Czochralski method (CZ method), for example.
2. Description of the Related Art
With regard to manufacture of semiconductor materials such as silicon through use of a pulling apparatus operated according to CZ method, there have been proposed various techniques for pulling a crystal safely through compensation for insufficient strength of a neck portion, or a portion of the crystal to be physically held and pulled, even when a large-sized or heavier crystal is pulled. The applicant of the present invention has also proposed such a single-crystal holding apparatus in, for example, Japanese Patent Application No. 7-351275.
As shown in FIG. 6, the single-crystal holding apparatus includes a wire pulling mechanism 52 for winding up a wire 51 and a lifting-jig moving mechanism 54 for vertically moving lifting jigs 53 which hold a corrugated portion Ck of a crystal C. A seed chuck 55 which holds a seed crystal 56 is attached to the tip end of the wire 51.
Initially, the seed crystal 56 attached to the tip end of the wire 51 is brought into contact with material melt, and subsequently the wire 51 is pulled by the wire pulling mechanism 52 to thereby grow the crystal C subsequent to the seed crystal 56. When the corrugated portion Ck formed between the seed crystal 56 and a straight cylindrical portion Ct of the crystal C rises to a predetermined position, bottom chuck portions d of a pair of lifting jigs 53, which have been in the open position, move inward and chuck the corrugated portion Ck. Subsequently, in place of the wire pulling mechanism 52, the lifting-jig moving mechanism 54 is operated so as to pull the crystal C.
The pair of lifting jigs 53 are pivotally supported at their intermediate pivotal point p and thus assume a scissors-like structure. Drive means 57 connected to the upper ends of the lifting jigs 53 cause the bottom chuck portions d to open or close.
Numeral 58 denotes a lifting base, which is part of the lifting-jig moving mechanism 54. Numeral 59 denotes a ball screw for moving the lifting base 58 vertically. Numeral 60 denotes a guide bar for guiding a vertical movement of the lifting base 58. Numeral 61 denotes an expandable bellows chamber.
However, in the crystal holding apparatus described above, the distance between the intermediate pivotal point p and a point of action (the tip end of the chuck portion d) is longer than that between a point of force generation (the drive means 57) and the intermediate pivotal point p. As a result, a small amount of play at the point of force generation (the drive means 57) becomes a large amount of play at the point of application (the tip end of the chuck portion d). This hinders a smooth switching from the wire pulling mechanism 52 to the lifting-jig moving mechanism 54.
Also, since the distance between the intermediate pivotal point p and the point of application (the tip end of the chuck portion d) is long, the lifting jig 53 easily deflects (deforms) due to a large load acting thereon or other causes. In this case, the chucking force decreases, so that a crystal slips out of position, resulting in a failure to grow a crystal having intended properties.
In the crystal pulling apparatus of FIG. 6, when the grown crystal C is to be unloaded therefrom, the bellows chamber 61 is contracted upward to expose the crystal C. In this case, since the ball screw 59 and the guide bar 60 are arranged around the bellows chamber 61, they may obstruct the removal of the crystal C from the crystal pulling apparatus.
Further, in a crystal pulling method wherein the bellows chamber 61 forms a vacuum chamber, an increase in the size of a bellows chamber associated with a recent tendency to increase the size of crystals requires the bellows chamber to have a sufficiently large strength against established vacuum and a large-sized drive to be provided for expanding/contracting the bellows chamber, involving difficult problems to solve.
Basically, the use of a bellows chamber is highly likely to involve a contamination of impurities caught in bellows into a crystal being grown, an insufficient degree of vacuum, turbulence in a flow of an inert gas, and other problems. Therefore, if possible, it is preferable that no bellows structure be employed.
Accordingly, in a crystal holding apparatus which holds a corrugated portion of a crystal by a lifting jig to thereby pull a crystal, there has been demand for a crystal holding apparatus capable of holding the corrugated portion reliably and without the occurrence of any play or displacement (variation in position stemming from slippage; the term "displaced" used hereinbelow has the same meaning) of a chucking position even when a relatively heavy load is imposed thereon.
In the case of a crystal pulling apparatus which employs a bellows chamber, it is preferable to employ a structure such that obstacles are not disposed around an area through which a grown crystal is taken out of the chamber.
Further, if possible, a crystal pulling apparatus preferably does not employ a bellows chamber itself.